Found an issue on NetScaler 10.5 build 54.9 which allows an SSL-Bridge vServer to be the target LB vServer of an SSL Content Switching vServer. If you leave this configured, it will crash the packet engine and the NetScaler will soft reboot.
This is not a supported configuration, but it should also not let you make said configuration in the NetScaler – this is fixed in build 57.7 – if not an earlier build. The GUI does not let you make this configuration.